Smooth attachment devices in insects: Functional morphology and biomechanics

In this chapter, I summarise the data collected in the literature on structure and mechanics of smooth attachment pads of insects. The ultrastructure, surface pattern, origin of different smooth pads, and their evolution are described. Results of mechanical testing of their material properties (elasticity, viscoelasticity, adhesion, friction) and basic physical forces contributing to adhesion are discussed. The influence of different factors, such as substrate roughness and stiffness of the pad, on contact forces is shown. Chemical composition of pad fluid, which is an important component of an adhesive function, is reviewed. Such structural features of pads, as anisotropic fibre orientation, hierarchical organisation of the fibrous architecture of the pads, and their surface microstructure are discussed in relationship to their mechanical effects. Data from insects are compared to those obtained from representatives of other animal groups, such as Echinodermata, Arachnida, and Mammalia. Finally, biomimetic implications of the results are briefly presented.